1. Field of the Invention
The present invention is generally related to a throttle position sensor and, more particularly, to a throttle position sensor that comprises a plurality of individual sensing elements that are combined to improve the resolution of the sensor and to provide an additional level of redundancy in the event that one of the sensors fails during operation.
2. Description of the Prior Art
Sensors are used in many applications to determine the position of one object relative to another object. In certain applications, a potentiometer is used and the movement of one object relative to the other, changes the effective resistance of the potentiometer and a voltage potential between two points of the potentiometer can be used as an indicator of the relative positions of the two objects. Position sensors are used in many different applications.
U.S. Pat. No. 5,445,126, which issued to Graves, Jr. on Aug. 29, 1995, describes an accelerator pedal calibration and fault detection. The invention automatically calibrates an electronic accelerator pedal having an idle validation switch. Automatic calibration accommodates variation between vehicles so that error tolerances may be reduced. The system and method utilize the idle validation switch in combination with the accelerator pedal to provide redundancy by cross-checking signals received from each component. Automatic calibration is performed through the operation of the vehicle. An initial idle position and an initial full throttle setting are chosen to induce a vehicle operator to fully depress the accelerator pedal. The fully depressed pedal determines the new full throttle position. Thereafter, under proper conditions, a new full throttle position is set when a pedal sensor indicates the current position exceeds the current full throttle set point. The system and method also provide a fail-safe design which returns to idle fueling when certain fault conditions are detected.
U.S. Pat. No. 5,321,980, which issued to Hering et al on Jun. 21, 1994, describes an integrated throttle position sensor with independent position validation sensor. The sensor includes electrically independent throttle position and position validation components responsive to a single mechanical input applied to a protective sensor housing. By suitable mounting to the throttle control device, the mechanical input corresponds to accelerator pedal position. Within the sensor housing, a potentiometer moves with the mechanical input whereby a variable voltage throttle position signal is generated. Also, within the housing a separate validation switch responsive to the mechanical input provides an independent representation of throttle control device position in the form of, for example, a bi-state validation signal. The sensor integrates previous separate throttle control position and position validation functions into a single environmentally secure housing which requires no calibration. The integrated sensor is more reliable and less costly than previously available separate throttle control and idle validation functions.
U.S. Pat. No. 5,438,516, which issued to Neubauer et al on Aug. 1, 1995, describes an integrated vehicle brake control device position sensor with precalibrated multiple sensor outputs. This device is generally related to the invention of U.S. Pat. No. 5,321,980.
U.S. Pat. No. 5,602,732, which issued to Nichols et al on Feb. 11, 1997, describes a fault tolerant displacement determination method.
Resolution of redundant displacement sensor information to form a displacement value in an automotive electronic throttle control system provides for a varying contribution by each of a plurality of redundant sensors to the formation of the displacement value in accordance with diagnosed variations in the fault status of the sensors. The number and type of fault conditions attributed to a specific sensor of the plurality over an analysis period are used to determine the relative degree by which that sensor will contribute to the displacement value formation. As an increasing number of fault conditions are attributed to a sensor, the relative degree of contribution of that sensor will gradually decrease. When severe fault conditions are attributed to a sensor, the relative degree of contribution of that sensor will rapidly decrease.
U.S. Pat. No. 5,669,353, which issued to Shirai et al on Sep. 23, 1997, described a valve feedback control having redundant valve opening sensors. A throttle control system has two throttle opening sensors. When one sensor in a PID feedback loop becomes abnormal, as sensed by monitoring the difference between outputs of the dual sensors, the use of sensor output for throttle feedback control is switched from the abnormal to the other, normal one. Which one of the throttle opening sensors has become abnormal is determined by monitoring the intensity of electric current flowing to a DC motor which drives the throttle valve. Further, if an abnormality in the newly used other sensor is determined, feedback control is continued based on an estimation of throttle opening calculated by using output of the sensor before its malfunction.
When sensors are used to determined the precise position of a manually movable member, such as a throttle control handle, it would be beneficial if a means could be provided to improve the resolution of the position reading so that very small movements of the manually movable member can be accurately detected with output signals that are sufficiently distinct to indicate those small movements of the manually movable member. It would also be beneficial if improved redundancy could be provided so that the failure of a single sensor would not disable the total sensing system.
A throttle position sensor made in accordance with the present invention comprises a manually movable member, such as a throttle handle, that is movable between a first end of travel in a first direction of travel and a second end of travel in a second direction of travel. For example, the throttle handle can be movable between a maximum forward setting and a maximum reverse setting. The throttle position sensor of the present invention further comprises a first sensor having a first output signal that is representative of the distance between the manually movable member and a generally central position which is located between the first and second ends of travel of the manually movable member. In other words, the first output signal represents distance that the manually movable member has moved from the central position, whether that movement is in a direction toward the first or second ends of travel.
The throttle position sensor also comprises a second sensor having a second output signal that is representative of the distance between the manually movable member and the first end of travel. In comparison to the first output signal, the second output signal represents the distance from one of the ends of travel and not from the central position.
The throttle position sensor of the present invention further comprises a controller that is connected in signal communication with the first and second sensors to receive the first and second output signals. The controller is configured to determine the position of the manually movable member as a combined function of both the first and second output signals.
Some embodiments of the present invention can further comprise a third sensor having a third output signal that is representative of the distance between the manually movable member and the first end of travel. The controller is connected in signal communication with the first, second, and third sensors to s receive the first, second, and third output signals. The controller is configured to determine the position of the manually movable member as a combined function of the first, second, and third output signals. It should be understood that the second and third sensors provide a degree of redundancy and, as such, the second and third output signals provide essentially the same information. The second and third sensors also provide a degree of redundancy with respect to the first sensor because either the second or third output signal can be used in place of the first output signal if the first sensor fails.
The first, second, and third sensors can comprise an analog-to-digital converter that converts a voltage signal to a digital output.